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Alternative Sorting

Last updated : April 17, 2025

What is Alternative Sorting?

Alternative sorting is a display format where the array is printed in a specific order. It has to be noted that it is not a sorting technique as the name falsely suggests, but rather an array representation.

Key Concept of Alternative Sorting

Given an integer array of size N, alternative sorting rearranges and displays the array such that:

• The largest element is placed at the first position (index 0),
• The smallest element is placed at the second position (index 1),
• The second-largest at the third position (index 2),
• The second-smallest at the fourth position (index 3),
• and so on…

Example

Input:
test1[] = {5, 3, 7, 1, 6, 0, 8, 9}
Output:
9, 0, 8, 1, 7, 3, 6, 5

Input:
test2[] = {-5, -3, 7, -2, 8, 0, -4, 0}
Output:
{8, -5, 7, -4, 0, -3, 0, -2}

Algorithm

• Sort the given array using an algorithm with time complexity of O(n log(n)), such as Quick Sort, Merge Sort, etc.
• Place a couple of pointers, one on the 0^th index and the other on the n-1^th index, to represent the minimum and maximum elements in the array.
• Print the pointer elements where the maximum element is printed first followed by the minimum element.
• Move the pointers towards each other by implementing decrement and increment.
• Continue the process until the pointers meet or cross each other.

Pseudo Code

Input Array: arr[] = {5, 3, 7, 1, 6, 0, 8, 9}
Sorted Array: arr[] = {0, 1, 3, 5, 6, 7, 8, 9}

int i=0, j=n-1;

while(i<j){
    print(arr[j--]+" ");
    print(arr[i++]+" ");
}
if(n%2 != 0){
    print(arr[i]);
}

C++ program to implement alternative sorting

#include <bits/stdc++.h>
using namespace std;

// Function to perform Alternative Sorting
void alternativeSorting(int arr[], int n)
{
    // Sorting the array
    sort(arr, arr + n);

    // Printing the element in alternative order
    // Right-most element first
    // Left-most element second
    // so on
    int i = 0, j = n - 1;

    cout << "Alternative Sorted Array : ";
    while (i < j) {
        cout << arr[j--] << " ";
        cout << arr[i++] << " ";
    }

    // If the total element in array is odd
    // then print the last middle element.
    if (n % 2 != 0)
        cout << arr[i];
}

// Main function
int main()
{
    int arr[100], n;
    
    cout << "Enter number of elements: ";
    cin >> n;

    for (int i = 0; i < n; i++) {
        cout << "Enter element " << i + 1 << ": ";
        cin >> arr[i];
    }
    
    alternativeSorting(arr, n);
    
    return 0;
}

Output

RUN 1:
Enter number of elements: 8
Enter element 1: 5
Enter element 2: 3
Enter element 3: 7
Enter element 4: 1
Enter element 5: 6
Enter element 6: 0
Enter element 7: 8
Enter element 8: 9
Alternative Sorted Array : 9 0 8 1 7 3 6 5 

RUN 2:
Enter number of elements: 9
Enter element 1: -5
Enter element 2: -3
Enter element 3: 7
Enter element 4: -2
Enter element 5: 8
Enter element 6: 0
Enter element 7: 0
Enter element 8: -4
Enter element 9: 1
Alternative Sorted Array : 8 -5 7 -4 1 -3 0 -2 0